Variable attenuator



Aug. 23, 1932.. H, R, HUNKlNs 1,872,954

VRIABLE ATTENUATOR Filed oct. '29, '1930 2 sheets-sheet 2 ATTENUATION DB OHMS RESISTANCE INvEN-roR HARoLo R. HuNmNs ATTONEY Patentecl Aug. 23,` 1932 ii UNITED STATES* PATENTfoFF-lc mon) n. HUNxINsfor BBoo'xLYN, VNEW Yonx, AssIGNoR 'ro INTERNATIONAL com-` v TIoN or NEW Yonx i z nA'rED, or vNEW Yonx, N. Y., A1 ochrona;

VABIABLE ATTENUATOB vA15,iiatnnr med October za, liaao.y serial No. 491,908.

This invention relatesto transmission systems and; part-icularly to devices for adjusting the attenuation; losses inV said system.

An object of the invention is to provide an,

attenuation'control device which will insert attenuation in smooth and gradual'steps between two transmission lines connected thereto. i V

Anotherffobj ect of vthe invention is thatsaid attenuationdevice shall insert efqual incre- Inents'of attenuation'for equal increments of angular rotationyof its Operating dials. i

, Another object. of the invention isthat said attenuation device shall' present'a constant impedance in one'or both directions toward the transmission lines'V to `Vwhich thesame is connected, as desired.v

Another'obfect of my invention is the provision offan attenuation control device wherein there is a plurality of continuously variab'le resistancelelements arranged to be adjustedso that the electrical network "incor-. porating'` said elements willinsert; transmission lossbetween circuits connected thereto, said loss being continuously variable between definite limit. y `i f Other. objectszand advantages of my inventio'n, together with certain details of construction and combinations of parts, willbe fully set forth Vthes}fecificatiori and pointed out in the appended claims. i I In' the draw'ingsz" I k f I f Eifgflisa perspcctive view of tone section of'aV device according to my'invention, showing` a'single resistance'coil; i a' i' Fig; 2 is a'perspective view ofanother section of said deviceshowing two resistance coilsconcentrically arranged; 4 i i Fig. 3 is a side elevational viewl offthe entire device' with the means for Operating the contactarms;

z Fig. ,4 is a view taken online of. Figi.` 3

" showingan operating'knob;

.F A, B, C, D, E are'schematic Vdiagrams showing five possible configurations ofV resistance :elements .into Vatte'nuation: networks,f which may :be phy'sically realized through :proper :combinations of` individual resistancel elements of the types showniin Figs. 1 to4'incl11sive.

Figz- 6 is a set 'of curves indicating the nianner in which the values of resistance as shown in lFi'g; 5A for example, vary' for various degrees of angular rotation of theV Correspondingt shafts from zero position. variations of the resistance of the coils shown in I `ig ;s.` 1 and 2 are realized'by windingsai'd coils on tapered forms, as illustrated in said drawings. w i

Figs. 7 and 8 show two of these `coils. The same characters indicate 'thef same parts throughout'the several views of Figs. 1 to 4 and similarly of Figs. 5 and 6. f

V With regard to the drawings, V'wherein'the preferred embodiment of niy invention' is disclosed, reference number 5) indicates a base or support of any suitable materialV tol which-is secured a hollow cylinder 6 preferably of bak'elite. The cylinderv has integral therewith a flange 7 and axialbearing'member 8. i

4Mountedon 'the cylindrical member 6 is a resistancev coilw9 wound upon Va suitable dielectrict after the manner described hereinafter. Ashaftll in bearing V8 has rigidly fixed thereto in anybvsuitable manner, such as by `a set screw' (not shown) ,z a wiping contact arm 12 which cooperates with the resistance element 9 to adjnst the -value`thereof, as well, understood in the art;` The stops`13 are provided to limit the travel of the contact arm12.f so ,a i w vTheV base v5 haseapertures 14 which are adapted to'receive the reduced, threaded ends ofzthe'spacers 1,5,` the opposite ends of which are rigidly fixed to another support or base 16. a To secure to the base 5 the spacers 15, nuts (not shown) Vare employed. The relative positions ofthe bases 5 and 16 are illustrated in Figs. 2 and 3.v w

A cylinder 17, similar to cylinder 6, is suitably secured to base 16and has integral therewith an axial bearing member 18. Two resistance coils 19 and 21 concentrically arranged andvpreferably insulated from each oc) i ioo A hollow shaft 22, through which shaft 11 extends, is journalled in bearing 18 and carries at one end a wiper 28 which is bifurcated to form two fingers 211 and 25 of unequal length, the former being bent out of the plane of the wiper 23 to cooperate with resistance coil 19. Finger 25 is adapted to slide along an edge of resistance coil 21. The edges of the two coils are not in the same transverse plane, but coil 21 projects beyond coil 19.

Operating handles 26 and 27 are attached to shafts 22 and 11, respectively. Pointers 28 and 29 indicate on a scale (not shown) the relative positions of the contact arms of wipers 12 and 23 with respect to the resistance coils. lVhen said shafts are operated so that said pointers are both at one end of the scale, the contact arms will be in a position such that the attenuation loss introduced by the device will bc a. minimum. Similarly, when the Operating handles are turned to the other` extreme position, the attenuation loss introduccd by the device will be a maximum. Further, setting of the Operating handles to any point between its limits of rotation will introduce attenuation losses in the device of an amount between the minimum and maximum Proportional to said degree of rotation, and the Variation of attenuation loss will be continuous from one setting of the Operating handles to another.

Coils 9, 19 and 21 are connected as shown at '1, a: and w' respectively in Fig. 5A. In Fig. 5B there are two coils such as 19 at w and w and two such coils as 21 at w' and 03'. Fig. 5G shows one coil like the coil 19 at w and two coils such as coil 9 at 3/ and y'; while Fig. 5D is similar to Fig. 5G with the coil 21 (02') in the opposite side of the Circuit. In Fig. 5D the arrangement is as in Fig. 5A with coil 21 omitted.

Artificial lines used as attenuation networks are generally of one of the forms shown in Figs. 5A, 5B, 5G, 5D and 5E. Inasmuch as it is customarily desired to introduce real attenuation without change of phase, the impedance elements indicated as w, m' and y may consist of non-inductive resistances. Consider for example the case shown in Fig. 5A, commonly called a T-typo artificial line. In order that the characteristic impedance of the network be solne constant value` ZO ohms, and the attenuation loss inserted thereby be N decibels, it is necessary that the resistance elements be determined from the formula:

(l-n) (1+n) The resultant values of x, m' and 'J for various values of Ndb when plotted, result in curves of the same general form as indicated in Fig. 6.

The characteristic impedance of the combination including the three elements w, w' and y, viewed from the input end, is constant; for the various positions of the operating knobs but the attenuation loss through the combination or network varies from a minimum to a maximum over the range of adj ustment as indicated by the curve marked Attenuation loss in Figure 6.

In accordance with this invention, the advantage of an attenuation device providing smooth and gradual variations in the amount of attenuation loss inserted, as contrasted to existing types of artificial lines in which the inserted attenuation loss is adjusted in comparatively large and discrete Steps, is realized by providing resistance elements of such a nature that the Variation of the resistance inserted in the w, w' and y arms follows the our-Yes af, af' and z/ in Fig. 6. This is accomplished physically by Winding the resistance elements on tapered forms with slidinq' contacts. Coils 19 and 21 are each wound on a tapered form 31, having straight sides, as shown in Fig. 7. Coil 9 is wound on a tapered form 82, having one concave side 33, as shown in Fig. 8. Form 32 is then mounted on hollow cylinder 6 and clamped at its ends by means of strips 13 and suitable nuts and bolts. Coils 19 and 21 are mounted in like manner on cylinder 17. The projecting ends of the clamping strips form the stops for the arms 12 and 23.

The arms 12 and 23 turn together in the same direction. As the resistance of coils 9 decreases in smaller steps, that of coils 19 and 21 each increases by larger amounts.

lVhile an arrangement has been set forth wherein the series and shunt elements are Controlled by separate knobs attached to concentric shafts, it is to be understood that the invention is not limited to the specific apparatus shown, but is applicable to cases wherein the elements are varied simultaneously through the use of aV common shaft.

It is of course obvious that the invention is not only adapted to insert attenuation loss between two transmission lines but is of equal utility as a means of adjusting the energy level at various points in transmission systems employing devices for producing, amplifying and translating electrical energy.

What is claimed is:

1. A variable attenuator comprising tapered forms and resistances wound on said tapered forms, said forms being mounted upon a cylinder in layers so that one of said forms projects beyond the other for contact purposes.

2. A variable attenuator comprising a tapered form having rectilinear sides, a resistance wound on said tapered form, a second 1,87a,os4

tapered form having at least one curvilinear side, and a resistance wound on said last mentioned form, both of said forms being cylindrically mounted so that one Projects' beyond the other for contact purposes' 3. A variable attenuator comprising ta.- pered forms having rectilinear sides, series resistances Wound on said tapered forms, a tapered form having at least one curvilinear side, and a shunted resistance wound on said last mentioned form, both of said forms beingV cylindrically mounted so that one pro-- jects beyond the other for contact purposes.

4. A variable attenuator comprising ta- HAROLD R. HUNZKINS. 

